Java Server Pages Design. Design Strategies

Transcription

1 Java Server Pages Design Jeff Offutt SWE 642 Software Engineering for the World Wide Web sources: Professional Java Server Programming, Patzer, Wrox, Ch 11 Design Strategies Many dozens of design strategies have been developed for web applications This lecture introduces two : 1. Page-centric : s are made to s, and the s respond to clients 2. Dispatcher : s are sent to s or servlets that then forward the requests to another or servlet In both cases, the goal is to separate logic from presentation and to separate as many concerns in the logic as possible 1 November 2013 Offutt 2 1

2 (1) Page-Centric Design Server Browser on a client Browser on a client or servlets Client requests are handled here EJB Java << Uses or instantiates >> Database Browser on a client 1 November 2013 Offutt 3 (1) Page-Centric Design cont. This is a simple design to implement The author can generate pages easily Two variants : Page-View Page-View with a Bean Does not scale up very well to large web sites Often results in a lot of Java code in the authors must be Java programmers Design is hard to see Hard to maintain 1 November 2013 Offutt 4 2

3 (1-A) Page-View Design A page and some back-end business processing Simple but not sophisticated or scalable Processing 1 November 2013 Offutt 5 (1-B) Page-View with Bean Design When more business processing and data access is needed Let Java handle the data Separates programming (Bean) from presentation () Processing 1 November 2013 Offutt 6 3

4 (2) Dispatcher Design A dispatcher accepts requests and routes them to the correct place Front-end (or servlet) looks at a portion of the request, and then chooses the correct place to forward it This is more sophisticated than the page-centric : More flexible and scalable More overhead that is wasted with small applications Three versions Mediator-View Mediator-Composite View Service to s 1 November 2013 Offutt 7 (2-A) Mediator-View Design The Mediating sends requests to a The sets and gets beans and creates a response page Mediating Presentation Presentation Delegate Processing Presentation 1 November 2013 Offutt 8 4

5 (2-B) Mediator-Composite Design The mediator-view helps with dynamically changing data, but sometimes the structure around the data changes Consider a web site that sells books, CDs, and videos The title, author and price form the data The structure will be different with each type of item With a mediator-view, the has to be changed to introduce new types of products The mediator-composite architecture allows nesting of s and HTML 1 November 2013 Offutt 9 (2-B) Mediator-Composite Design Mediating header body footer header body footer changeable Delegate Enterprise Java Back-end resource 1 November 2013 Offutt 10 5

6 (2-B) Mediator-Composite Design In this architecture, the makes direct calls to the business logic modules This creates a tight coupling between the and the execution or business logic In the next architecture, the is separated further from the business logic modules 1 November 2013 Offutt 11 (2-C) Service to s Design Service Mediating Biz Delegate s Java Bean Resources EJB 1 November 2013 Offutt 12 6

7 (2-C) Service to s Design The mediator sends requests to worker beans The worker beans use the back-end software to populate the beans with data The s then take the data and create output pages This method breaks up the view and the controller Useful when many methods are needed to generate the data 1 November 2013 Offutt 13 Summary Web App Design Strategies Many design patterns and design strategies exist And new patterns are created all the time Each pattern helps make certain parts of the web app easier to change, at the expense of others They are designed to support one or more engineering goals : Reliability Usability Security Availability Maintainability Performance 1 November 2013 Offutt 14 7